//最小覆盖子串
public class MinWindow {
    public String code(String ss, String tt) {
        char[] s = ss.toCharArray();
        char[] t = tt.toCharArray();

        int[] hash1 = new int[128];
        int kinds = 0;
        for (char ch : t){
            if (hash1[ch] == 0){
                kinds++;
            }
            hash1[ch]++;
        }

        int minlen = Integer.MAX_VALUE, begin = -1;
        int[] hash2 = new int[128];
        for (int left = 0, right = 0, count = 0; right < s.length; right++){
            char in = s[right];
            hash2[in]++;
            if (hash2[in] == hash1[in]){
                count++;
            }

            //出窗口
            while (count == kinds){
                if (right - left + 1 < minlen){
                    minlen = right - left + 1;
                    begin = left;
                }

                char out = s[left++];
                if (hash2[out]-- == hash1[out]){
                    count--;
                }
            }
        }

        if (begin == -1){
            return new String();
        }else{
            return ss.substring(begin, begin + minlen);
        }
    }
}
